By means of N-body simulations we study the ion and electron dynamics in molecular first-row hydride clusters when exposed to intense and short X-ray pulses. We find that, for a particular range of X-ray intensities, fast protons are ejected from the system on a considerably shorter time scale than that of the screened core. As a consequence, the structure of heavy atoms is kept intact", which may be relevant in the context of X-ray based molecular imaging. Moreover the final charge states of the heavy ions are considerably lower than those of the ions in pristine atomic clusters exposed to the same laser pulses, which is in agreement with recent measurement of methane cluster at the LCLS in Stanford.

The interaction of intense laser pulses with nanometer scale atomic clusters has been an active area of study since the advent of amplified femtosecond lasers. In the case of infrared irradiation of noble gas clusters, direct field-driven ionization results in the ejection of energetic electrons, high ion charge states, and Coulomb explosion of the ion core of the clusters. These processes result from electron motion driven by the cluster potential and the large ponderomotive potential of the laser field. When extreme ultraviolet (XUV) pulses interact with clusters, the mechanisms responsible for the infrared response are 'turned off' because the ponderomotive potential is very small. We have conducted cluster experiments at 38nm using focused XUV pulses produced by high harmonic generation with a 15TW Ti:Sapphire laser. We measured the charge states and kinetic energy spectra of ions produced in the interaction, and observe substantial ion population up to Xe⁵⁺, with a small number of Xe⁶⁺-Xe⁸⁺ ions produced by collisional ionization by hot plasma electrons. The ion kinetic energy spectrum indicates a hydrodynamic expansion at an ion temperature of 8eV. This is in stark contrast to intense infrared/cluster interactions, where clusters are stripped of electrons to a large degree and expand by Coulomb forces, resulting in far higher ion kinetic energy for similar degrees of ionization. / text

No description available.

The dynamics of atomic scale structures during structural change can be studied by Ultrafast Electron Diffraction (UED). The time resolution needed to reveal the fastest dynamics is 100 fs. Sub-angstrom structural resolution becomes possible with 1-1000 pC of charge necessary for diffraction pattern analysis during subtle structural changes. This combination of requirements cannot currently be realized due to the space-charge temporal broadening inherent to bunches of electrons of high fluence and short temporal duration. Simulations show that the incorporation of a specially designed Radio-Frequncy (RF) cavity into the UED apparatus removes this technical limitation. The RF cavity reverses the near linear position-momentum distribution of the temporally broadened electron bunch, causing the bunch to recompress itself as it propagates. It is found that our proposed method allows for sub-100 fs bunches with maximum charge of 0.6 pC, almost 3 orders of magnitude improvement over today's state of the art.

Femtosecond time-resolved photoelectron spectroscopy (fsTRPES) experiments have been used to study the photoelectron energy spectra of simple molecules since the 1980’s. Analysis of these spectra provides information about the ultrafast internal conversion dynamics of the parent ions. However, ultraviolet pulses must be used for these pump-probe experiments in order to ionize the molecules. Since current solid state lasers, such as the Ti:sapphire laser, typically produce pulses centered at 800nm, it is necessary to generate UV pulses with nonlinear frequency mixing techniques. I therefore constructed an optical setup to generate the 3rd and 4th harmonics, at 266.7nm and 200nm, respectively, of a Ti:sapphire (Ti:sa) chirped-pulse amplified (CPA) laser system that produces 35fs pulses centered at 800nm. Thin Beta-Barium Borate (β-BaB2O4 or BBO) crystals were chosen to achieve a compromise between short pulse durations and reasonable conversion efficiencies, since ultrashort pulses are quite susceptible to broadening from group velocity dispersion (GVD). Output energies of around 11μJ and 230nJ were measured for the 266.7nm and 200nm pulses, respectively. The transform limits of the 3rd and 4th harmonic pulse lengths were calculated from their measured spectral widths. We found that the 266.7nm bandwidth was large enough to support sub-30fs pulses, and due to cutting at the lower-wavelength end of the 200nm spectrum, we calculated an upper limit of 38fs. The pulses were compressed with pairs of CaF2 prisms to compensate for dispersion introduced by transmissive optics. Two-photon absorption (TPA) intensity autocorrelations revealed fully compressed pulse lengths of 36 ± 2 fs and 42 ± 4 fs for the 3rd and 4th harmonics, respectively.

This thesis contains three components of research: a detailed study of the performance of Frequency-Resolved Optical Gating (FROG) for measuring complex ultrashort laser pulses, a new method for measuring the arbitrary polarization state of an ultrashort laser pulse using Tomographic Ultrafast Retrieval of Transverse Light E-fields (TURTLE) technique, and new approach for measuring two complex pulses simultaneously using PG blind FROG. In this thesis, we compare the performance of three versions of FROG to measure complex ultrashort laser pulses: second-harmonic-generation (SHG) FROG, polarization-gate (PG) FROG, and cross-correlation FROG (XFROG). We found that the XFROG algorithm achieves 100% convergence, while PG FROG and SHG FROG GP algorithm achieve 100% convergence after doing the noise deduction and increasing the sampling range. The second part of this thesis describes a method for measuring the intensity, phase and the complete polarization state of a laser pulse having a time-dependent polarization state (i.e. a polarization shaped pulse). This technique is called tomographic ultrafast retrieval of transverse light E-fields (TURTLE). TURTLE typically involves making three FROG measurements: one of the intensity and phase of the pulse's horizontal polarization component, one of its vertical component, and another of the 45o component. Performing a simple minimization using these three FROG measurements, the time-dependent polarization state of the ultrashort pulse can be determined. The third part of this thesis introduces a method for measuring two complex pulses simultaneously using a single FROG device. This technique is based on Polarization-gate (PG) FROG and it is called PG blind FROG. It involves two measurements: One of them is a PG FROG trace using the intensity of pulse 1 to gate pulse 2 and other one is the PG FROG trace using the intensity of pulse 2 to gate pulse 1. An iterative phase retrieval algorithm based on generalized projection (GP) is used to reconstruct the intensity and phase of these two pulses. This approach is an elegant way to measure complex and/or very spectrally broad pulses such as those due to super continuum.

Thesis (M.App.Sc.) - Carleton University, 2007. / Includes bibliographical references (p. 86-94). Also available in electronic format on the Internet.

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Includes bibliographical references (p. 121-127).

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 198-205).

Submitted by Luciana Ferreira (lucgeral@gmail.com) on 2016-02-01T08:04:44Z No. of bitstreams: 2 Dissertação - Vinícius Vaz da Cruz - 2015.pdf: 2292478 bytes, checksum: 170721177f0dc0267e59c8d54868ae20 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2016-02-01T08:06:56Z (GMT) No. of bitstreams: 2 Dissertação - Vinícius Vaz da Cruz - 2015.pdf: 2292478 bytes, checksum: 170721177f0dc0267e59c8d54868ae20 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Made available in DSpace on 2016-02-01T08:06:56Z (GMT). No. of bitstreams: 2 Dissertação - Vinícius Vaz da Cruz - 2015.pdf: 2292478 bytes, checksum: 170721177f0dc0267e59c8d54868ae20 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Previous issue date: 2015-08-28 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / This dissertation presents a wavepacket simulation study of the H + HCl collinear reaction when the HCl molecule is initially prepared by an infrared laser pulse in a coherent superposition of vibrational states. A detailed discussion of wavepacket motion, reactive flux and reaction probabilities as function of the superposition state parameters is presented. We apply the flux formalism to derive an analytical expression for the reaction probabilities, which is then used to analyse our numerical simulations. The results show a strong phase dependence of the reaction probabilities, as well as the spatial distribution of the reactant molecules. The full reaction probability surface is computed for two average collision energies, and the enhancement and suppression of the H+HCl!H2+Cl reaction channel is discussed in terms of the surface’s critical points. / Esta dissertação apresenta o estudo por meio de simulações de pacote de ondas das colisões colineares H + HCl quando a molécula de HCl é preparada por pulsos de laser de infravermelho em uma superposição de níveis vibracionais. É feita uma discussão detalhada do movimento do pacote de ondas, fluxo reativo e probabilidades de reação em termos dos parâmetros da superposição de estados. Nós aplicamos o formalismo de fluxo para deduzir uma expressão analítica para as probabilidades de reação, a qual é então utilizada na análise de nossas simulações numéricas. Os resultados mostram uma grande dependência das probabilidades de reação com a fase e com a distribuição espacial das moléculas reagentes. A superfície completa de probabilidade de reação é calculada para duas energias de colisão médias, e as condições de melhora e supressão da reação H+HCl!H2+Cl é discutida em termos dos pontos críticos da superfície.